1. Field of the Invention
This invention relates to an apparatus for operating a cover for a manhole for operating and inspecting piping, a tank or the like which is laid under the ground, and more particularly to a novel apparatus for operating a manhole cover which is effectively applicable to a manhole cover of any shape and adapted to readily carry out both the separation of an edge of a manhole cover securely adhered to a support frame of a manhole therefrom and the subsequent lifting and movement of the cover from the manhole.
2. Description of the Prior Art
In general, a manhole cover is provided with various types of holes for operating the cover depending upon the type of manhole. Also, a manhole cover generally has a large weight and is fitted in a support frame of a manhole in a state of being adherently fixed therein by means of sand, mud or the like entering between the cover and the support frame. Accordingly, in order to operate an manhole cover, it is initially required carry out the separation of an edge of the manhole cover from a support frame of a manhole which is generally referred to as "edge separating operation" in the art, prior to the opening of the manhole cover. Such edge separating operation renders the operation of a manhole cover highly troublesome.
More particularly, a manhole cover, as shown in FIG. 1, is provided with various types of operating holes depending upon the type of a manhole cover. In FIG. 1, reference numeral 20 designates a manhole cover and 22a to 22f indicate operating holes formed at the manhole cover 20. In general, such operating holes each are generally arranged in the circumferential direction of a manhole cover. For clarity in the description, in FIG. 1, a single manhole cover 20 is provided with all kinds of operating holes 22a to 22f. Normally, one or two such types of operating holes are selectively provided at a manhole cover depending upon the type of a manhole cover. Operating holes as designated by reference numerals 22a and 22b in FIG. 1 are of the type defined by British Standard. The operating holes 22a and 22b each are formed to have a central circular portion and a pair of extensions outwardly radially extending in the opposite directions therefrom, so that such a hanging hook as generally indicated by reference numeral 24 in FIG. 1 which is constructed to have projections 26 provided on both sides of a lower end thereof may be fittedly engaged at the lower portion thereof therein. The operating holes 22a and 22b are formed in the directions perpendicular to each other along the circumference of the manhole cover 20.
An operating hole of such type as indicated by reference numeral 22c comprises a blind hole portion having a round bottom and a rectangular planar shape and a rod portion provided in a manner to be laid across the blind hole portion to separate the surface of the blind hole portion into two sections, so that such a hanging hook as generally designated by reference numeral 28 in FIG. 1 may be engaged with the operating hole 22c in a manner such that a hook portion 30 of the hanging hook 28 is engaged with the rod portion of the operating hole 22c to scoop the manhole cover 20. The rod portion of the operating hole 22c is formed so as not to project from the surface of the manhole cover. Also, the rod portion is generally formed to be integral with the manhole cover. An operating hole 22d is of the so-called hatch-type and comprises a blind hole portion and a handle provided in a manner to be retractable with respect to the manhole cover 20. The operating hole 22d likewise is used for a hanging hook of such type as indicated by reference numeral 28.
Operating holes indicated by reference numerals 22e and 22f in FIG. 1 each are of the so-called pick-hole type and typically provided at a cover for a manhole for water supply and drainage, a telephone line or the like in the United States. Such operating holes are formed into a simple circular or rectangular shape, in which a tip end of a pick is insertedly engaged to openably operate the manhole cover. The operating holes 22e and 22f are inferior in workability to those indicated by 22a to 22d.
In general, an apparatus for operating a manhole cover falls under the category of a portable tool, therefore, it has been conventionally required to restrict the overall length of the apparatus to at most about 1 m. This renders the use of the apparatus as a lever in such edge separating operation as described above highly troublesome or substantially impossible.
More particularly, the manhole cover edge separating operation, as shown in FIG. 2, requires lifting force of 1000 kg or more. In a typical manhole cover operating apparatus which has been conventionally used, operating holes each are provided at a position spaced inwardly by a distance of 8-10 cm from an outer periphery of the manhole cover. The maximum distance often mounts up to about 15 cm. Assuming that the lifting force of one operator is, for example, 60 kg and a manhole cover operating apparatus or lever which is used in the edge separating operation carried out under the above-noted circumstances has a length of, for example, 1 m and has a point of support positioned between a point of application and a point of force; the lifting of an edge of a manhole cover with force of 1000 kg in the edge separating operation requires the apparatus or lever to have a leverage of about 17. This requires the distance between a point of application and a point of support in the lever to be set at 5-6 cm. However, the setting of such a distance is substantially impossible because operating holes each are generally provided at a position spaced inwardly by a distance of 8-10 cm from an outer edge of a manhole cover, as described above.
Also, in order that the manhole cover of which the edge is lifted in such a manner as described above is removed and moved from a manhole, the manhole cover must be lifted by a distance sufficient to insert a roller between the ground and the cover, for example, a distance of about 10 cm. Unfortunately, in general, as the leverage of a lever is increased, the degree of lifting of a manhole cover is correspondingly reduced; accordingly, it is substantially impossible to carry out the movement of a manhole cover from a manhole subsequent to the edge separating operation.
Under the circumstances, in the operation of a manhole cover, the separation of an edge of a manhole cover securely adhered to a manhole by sand, mud or the like therefrom was carried out using not only a manhole cover operating apparatus but another means such as a hammer or the like, and the lifting and movement of the manhole cover from the manhole was carried out by means of separate special tools such as a lifter, a conveyor and the like as well as a manhole cover operating apparatus.
Such a conventional manhole cover operating apparatus as described above is exemplified in, for example, each of Japanese Patent Application Publication No. 46025/1978, Japanese Utility Model Application Laid-Open Publication No. 88452/1980 and Japanese Patent Application Laid-Open Publication No. 173227/1983. Unfortunately, the conventional manhole cover operating apparatus disclosed in the publications are limited to the use for only a manhole cover having operating holes of such type as defined in British Standard or indicated by reference numerals 22a and 22b in FIG. 1 and cannot be applied to operating holes of the pick-hole type as indicated by reference numeral 22e and 22f in FIG. 1. Also, the conventional apparatus each are directed to the movement of a manhole cover removed from a manhole and not suitable for use for the separating and lifting of an edge of a manhole cover from a manhole.
In view of the foregoing, the inventors proposed such a manhole cover operating apparatus as disclosed in Japanese Patent Application Publication No. 44505/1974. The apparatus disclosed is constructed to have a wheel incorporated therein which acts as a point of support to open a manhole cover. Unfortunately, the apparatus is applicable to only a manhole cover having two operating holes provided on its center-of-gravity line, for example, typically its diameter line and at a position near its outer periphery thereof, therefore, it is never used for a manhole cover locally provided with a single operating hole of the pick-hole type.
Accordingly, it would be highly desirable to develop an apparatus for operating a manhole cover which is capable of being applied to a manhole cover formed with operating holes of any shape or type and carrying out the separation of an edge of a manhole cover securely adhered to a support frame of a manhole therefrom and the lifting of the separated edge from the manhole as well as the movement of the manhole cover from the manhole.